Insight into the formation mechanism of higher-molecular-weight gases during the spontaneous combustion of coal

Abstract

Higher-molecular-weight gases (HMWGs), which have not received much attention, also contain invaluable information about the coal spontaneous combustion (CSC) development process. In order to investigate the formation mechanism of HMWG, the emission behaviors of HMWG from coal oxidation and pyrolysis experiments were compared, and FTIR and ESR were used to analyze the microstructural evolution of the coal sample. The results show that the volume fractions of most HMWGs increased regularly with increasing temperature. The contribution of the pyrolysis process to the yield of most hydrocarbon HMWGs was close to 100 %, while it was below 89 % for C₄ ∼ C₆ n-alkanes and benzene and less than 10 % for acetaldehyde and acetone. The decomposition of active structures could produce free radicals, the concentration of which increases with increasing temperature. The formation mechanism of HMWGs was proposed based on the experimental results: HMWGs came from both the thermal reaction and the coal-oxygen reaction process. The thermal reaction process would release the majority of hydrocarbon HMWGs from room temperature. Some active structures began participating in the coal-oxygen reactions to produce oxygen-containing HMWGs at 90 ℃. After reaching 170 ℃, the coal-oxygen reactions were further intensified to release minority n-alkanes, benzene, and small amounts of C₄ olefins.